Shammah or Shimea

Shammah - 1 Samuel 16:9; 17:13 Jesse then had Shammah pass by, but Samuel said, Nor has the LORD chosen this one.... Jesses three oldest sons had followed Saul to the war: The firstborn was Eliab; the second, Abinadab; and the third, Shammah.

Shimeah - 2 Samuel 13:3; 21:21 Now Amnon had a friend named Jonadab son of Shimeah, David's brother. Jonadab was a very shrewd man.... When he taunted Israel, Jonathan son of Shimeah, David's brother, killed him.

Shimea - 1 Chronicles 2:13; 20:7 Jesse was the father of Eliab his firstborn; the second son was Abinadab, the third Shimea.... When he taunted Israel, Jonathan son of Shimea, David's brother, killed him.

Because of regional patterns of pronunciation, plurality of names, etc. it is not uncommon for proper names to be spelled differently. As seen above (the list is not complete), there are variations of the name in many places in Scripture. Bible Dictionaries have different comments concerning the names:

A brother of King David, and son of Jesse (1 Sa. 16:9). Variant forms of the name are Shammua, Shimea, Shimeah, Shimeam and Shimei. 3. One of the outstanding three of David's warriors (2 Sa. 23:11), described as a Hararite. The Shammah of 2 Sa. 23:30 is almost certainly the same man, but there are textual problems; cf. NEB. 4. Another of David's warriors, a Harodite (2 Sa. 23:25). 1 Ch. 11:27 renders his name as Shammoth (a plural form of the name), and the Shamhuth of 1 Ch. 27:8 may well be the same man. (New Bible Dictionary)

The third son of Jesse and brother of David. Together with his two other brothers he fought under Saul in the campaign against the Philistines and was with the army in the valley of Elah when David slew Goliath (1 Samuel 17:13 ff). One redactor states that he was a witness of the anointing of David by Samuel (1 Samuel 16:1-13). He was the father of Jonadab, the friend of Amnon (2 Samuel 13:3 ff), and that Jonathan whose victory over a Philistine giant is narrated in 2 Samuel 21:20 ff was also his son. His name is rendered as Shammah (1 Samuel 16:9; 17:13), Shimeah (2 Samuel 13:3, 12), Shimei (2 Samuel 21:21), and Shimea (1 Chronicles 2:13; 20:7). (The International Standard Bible Encyclopedia)

Third-born of Jesse's eight sons, the brother of David and the father of Jonathan and Jonadab (1 Sm 16:9; 17:13). Shammah is alternately called Shimea in 1 Chronicles 2:13 (KJV Shimma) and 20:7, Shimeah in 2 Samuel 13:3, and Shimei in 21:21 (KJV Shimeah). (Baker Encyclopedia of the Bible)

The third son of Jesse, David's father, and one of the brothers not chosen by Jehovah to be anointed king (1 Sam. 16:9), before 1000 B.C. With his two elder brothers he joined the Hebrew army (17:13). He is elsewhere, by a slight change in the name, called Shimea (1 Chron. 2:13; 20:7) and Shimeah (2 Sam. 13:3, 32). (The New Unger's Bible Dictionary)

References

Wood, D. R. W., & Marshall, I. H. (1996). New Bible Dictionary (3rd ed.). Leicester, England; Downers Grove, Ill.: InterVarsity Press, 1996.

Orr, J., ed.The International Standard Bible Encyclopedia, 1915 edition. In Ages Software. Albany, OR., 1999.

Elwell, W. A., & Beitzel, B. J. Baker Encyclopedia of the Bible (1936). Grand Rapids, Mich.: Baker Book House, 1988.

Unger, M. F., Harrison, R. K., Vos, H. F., Barber, C. J., & Unger, M. F. The New Unger's Bible Dictionary (Rev. and updated ed.). Chicago: Moody Press, 1988.